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Leslie Spry, M.D., FACP Headshot

Kidney Donation: How Do You Match Up?

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April is National Donate Life Month, and if you're thinking about donating a kidney, now would be the time to find out what it's all about. Did you ever wonder how they match potential organ donors with people who need organs? There are more than 92,000 people in the United States who are waiting for a kidney transplant. More than 114,000 people are waiting for a lifesaving organ transplant of some kind. More than 16,000 kidney transplants were done last year and more than 5,000 of them were from live donors.

So what's the secret to the perfect match? I'll answer that question with a few more questions.

What's Your Type? We first need to know your blood type. The blood types are O, A, B, and AB. Certain blood types can only be matched to other blood types in a specific way. Blood type O is a universal donor who can donate to any person on the list. If you are the kidney recipient with blood type O, then you can receive a kidney from another blood type O donor. If you have blood type A, your donor must be blood type O or A. If you are blood type B, your donor must be blood type O or B. If you are blood type AB, your donor could be blood type AB or O. Blood type O is the most common blood type and blood type A is the second most common.

Is there a mismatch? An antigen is a protein that acts to label and to identify some unique aspect of every cell in your body. Every cell in the body has antigens that are unique to that person. The human leukocyte antigens (HLAs) are unique sets of proteins that identify each person as a unique individual to the immune system. Your immune system must search out foreign material, such as bacteria and viruses, and be able to distinguish these foreign "invaders" from your own cells. Antigens help your body to catalog what's foreign by providing a unique immunological "fingerprint" of your identity. So, in order to allow organ donation, it is important to try to match at least some of these HLAs to lessen the impact of your body perceiving the new organ as an invader.

An HLA typing laboratory determines antigens for each transplant patient and catalogs them into three different types: HLA-A, HLA-B and HLA-DR. The genes for these unique antigens are found on Chromosome #6, which you get from both your mother and father, making it possible to have a total of six antigens. You inherit one A, B, and DR antigen from your father and one A, B, and DR antigen from your mother. Your antigen type is compared against that of the donor to see how many match.

Unfortunately, we sometimes cannot type all antigens, so when we match, we also determine how many "mismatches" exist. If your mother or father donated to you, you would have three mismatches (out of six possible) with each of them. If your identical twin donates, you would have zero mismatches. If your friend donates, we look to see how many mismatches we can measure and then express that as the number out of a possible six matches. Fewer mismatches mean a greater chance of transplant success, which is why sometimes multiple people will get tested to be a living donor for one recipient.

Will your history work against you? Antibodies are immune proteins that attach to and attack the antigens on cells. For recipients, the HLA typing laboratory will try to determine how many pre-formed antibodies they carry around in the blood that might attack a prospective donor's organ. These pre-formed antibodies can come from prior transplants, blood transfusions and having babies. The antibodies are then expressed as the percentage of a broad variety of people that you might already have antibodies against in your blood stream. This is known as a Panel Reactive Antibodies (PRA) and is commonly expressed as a percentage of 100. For example if you have a PRA of 50, then you may already have pre-formed antibodies against 50 percent of the kidneys that may be available for you.

Are you a fighter? The final matching test is whether or not your blood cells and your donor's blood cells will react with each other. This test is known as a crossmatch. The crossmatch test tries to grow your immune cells with your donor's cells to determine if they will attempt to attack the new cells. If they attack the new cells, then the transplant will likely not be successful. This test must be done to make sure that the new organ will not be immediately attacked by the immune system of the person who is receiving the organ, because this could lead to acute rejection of the transplant.

Can we give the green light? Once all the test results are known, the transplant team must evaluate them together in order to weigh the pros/cons. Because not all of these tests are black and white, they must be interpreted by the transplant surgery team to make sure the transplant is in your best interest. The team will advise you as to the risks and benefits of proceeding with the surgery.

What's new? Transplant medicine has been coming up with ways to improve the chances of a successful transplant. Performing transplants in patients with pre-formed antibodies is very high risk, but experimental protocols have been developed to overcome this problem. Performing transplants with ABO incompatibilities require very complicated treatment protocols. Finally, new ways of changing the immune system by introducing immune cells from the donor to the recipient are being tried with varying success. We are trying to transplant as many patients as possible because transplantation will double the life expectancy of a patient with kidney failure compared to staying on dialysis.

For more information about organ transplantation and living donation, visit the National Kidney Foundation and the United Network for Organ Sharing.

For more statistics about organ donation and transplantation, visit the U.S. Department of Health and Human Services Organ Procurement and Transplantation Network.

For more by Leslie Spry, M.D., FACP, click here.

For more on personal health, click here.

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